This invention relates to internal combustion engines. More particularly, this invention relates to engine systems which sense the load being applied to the engine and which change an operating parameter, such as engine speed, fuel flow, or ignition timing, in response to the sensed load.
Internal combustion engines are often used to power a load, such as a pressure washer, a power drill, a chain saw, or many other tools and devices. Engines are also used to supply power to generators, which in turn operate compressors, construction equipment, and the like.
When an engine is used to power a load, the load is often not operated continuously. For example, a power drill may be used intermittently, even though the engine continues to operate. It is generally desirable to have the engine running at a relatively high operating speed when the load is being applied to the engine. When the load is not being used, it is often desirable to reduce the engine speed or to change another engine operating parameter to reduce fuel consumption, lessen noise, and extend the life of the engine.
To sense whether the load is being applied to the engine, prior art devices typically use a manifold pressure sensor, a hall effect sensor, or some other device that generates a signal which is functionally related to the magnitude of the applied load. Often, two sensors are needed: one to sense manifold pressure and one to sense throttle plate position. A disadvantage of such prior art devices is that the requirement for these sensors increases the cost and complexity of the system. When a sensor fails, the additional expense of a replacement sensor and the system downtime increase the effective cost of the system.
FIG. 1 is a block diagram of a typical prior art system. As shown in FIG. 1, a control module 10 receives signals which are indicative of engine position, engine temperature, and manifold pressure or throttle plate position. The control module interprets the signals to change one or more engine operating parameters, such as ignition timing, fuel flow, or engine speed.